Theoretical studies on force titration of amino-group-terminated self-assembled monolayers

The structures of (3-aminopropyl)triethoxysilane (APTES), 4-aminothiophenol (4-ATP) and 4-mercaptopyridine (4-MP) self-assembled monolayers (SAMs) are studied by quantum mechanics in order to explain the force titration curves of these amino-group-terminated SAMs. The surface charges and electrostatic surface potentials derived from the ab initio calculations can give satisfactory explanations for the experimental results. We also propose a simple model to simulate the force titration process. The force between the tip and sample can be estimated according to the slope coefficient of the curve of energy versus distance. This curve can lead to a better understanding of the force titration curves of amino-group-terminated SAMs.